To Applicant's knowledge, the only method for producing a shaped non-woven, namely a non-woven having, in cross-section, a shape which is not roughly rectangular, consists in making one or more slanted cuts in the non-woven, once the non-woven is produced. Although such cuts are feasible on non-wovens of a certain thickness and on the lateral faces thereof, they are nevertheless virtually impossible on the upper face. Therefore, it is difficult to obtain a non-woven having a cross-section which is not rectangular but for example trapezoidal.
It is the object of the present invention to propose a method for producing such a non-woven.
This method for producing a shaped non-woven comprises the step of feeding fibers to a carding machine, receiving the fibrous web leaving the carding machine and needling said web. The fibers are fed over a limited width of the carding machine and, moreover, the fibrous web leaving the carding machine is superposed into at least ten layers before needling.
Applicant has indeed found that when the fibers are not fed through the whole width of the carding machine, the edges of the obtained web are thinner than the mean thickness of said web. Said thickness difference is hardly noticeable on a unitary web leaving the carding machine. It is the merit of the invention to accentuate and draw advantage from this irregularity by controlling the feeding and by superposing unitary webs in the form of at least ten successive layers. In this way, the non-woven obtained has, in cross-section, a shape which is not rectangular. Some parts of the non-woven have a different thickness from the mean thickness of the web.
Relatively to the production of fibrous webs, document FR-A-2 598 723 describes a method and device for intermingling tapes of fibers notably at the level of carding machines. The method consists, after laying flat the fibrous tape, in intermingling the fibers of the tape by means of air jets so as to improve cohesion of the tape. To this effect, the apparatus comprises, in addition to the air injecting nozzles, a funnel of tape of which the edge has a cross-section reducing in the tape-conveying direction, and a device for guiding the fibers, which device is placed at the front of the funnel.
Another device is described in document DE-A-2 437 176, and is able to produce a fibrous web from a raw material constituted of fibers. In this device, the fibers, once introduced, are conveyed through a cavity under the action of an air stream, up to two perforated rollers of parallel axes. The fibers, having thus been sucked in, are applied against said rollers which rotate respectively in opposite directions. The fibers then pass between the two rollers where they mingle together in order to constitute the fibrous web. The orientation of the side walls of the cavity where the fibers pass through is adjustable, so as to obtain a fibrous web of given width.
It is not possible, with the two aforesaid known devices, to obtain a fibrous web with edges thinner than the mean thickness of the web. Therefore, the winding of the resulting web will not give a shaped non-woven as does the present invention.
A method and apparatus are also known from document EP 0 147 297, for producing structures formed by superposed layers of fibrous material, joined one to the other. To this effect, a strip of material is brought over a rotary mandrel, so as to be wound thereon it into successive overlapping spires. However, two successive spires are not superposed, as with the method according to the present invention. Moreover, the successive parts of the strip of material have generally been pre-needled for strengthening purposes, which makes them easier to handle.
Another method and device are also known from document CH-A-350 584 for directly winding on a winding machine, a strip of cotton leaving a carding machine. Said cotton strip has been strengthened prior to winding by passing between two rollers of a heated pre-shaping calendering machine. Admittedly, the cotton strip is wound in successive superposed layers, but as these layers have already been strengthened, the strip is not needled.